The present invention relates to a process for manufacturing a composite sheet comprising a web capable of elastic stretch and contraction and a fibrous web capable of inelastic extension.
Japanese Patent Publication No. 1996-504693A discloses a multi-layered elastic panel, as one example of this type of composite sheet, and a process of manufacturing the same. The disclosed manufacturing process of a multi-layered elastic panel involves arranging a rubber elastic layer and an inelastic fibrous layer, one over another, joining them intermittently, extending the combination up to the vicinity of a breaking extension limit of the inelastic fibrous layer and finally relaxing the combination from tension.
In the composite sheet (elastic panel) obtained via the above-specified known manufacturing process, the rubber elastic layer after removal of the tension is unable to return to its original dimension. The resulting difference in dimension sometimes produces a permanent strain in the composite sheet. Such a permanent strain is a first factor that makes the composite sheet larger in dimension along a direction of extension than before it is subjected to extension. Also, the inelastic fibrous layer when extended undergoes plastic deformation so that its dimension after extension is made larger than before extension. When the rubber layer is relaxed from the tension, this dimensional difference causes the inelastic fibrous layer to increase its apparent bulk. The increased bulk then becomes a second factor that makes the composite sheet larger in dimension than before it is extended by restraining the rubber elastic layer from relaxing, i.e., by restricting elastic contraction thereof. By these first and second factors, the composite sheet when again extended to the vicinity of a breaking extension limit of the inelastic fibrous layer shows a lower percentage extension than when initially extended to the vicinity of the breaking extension limit of the inelastic fibrous layer.
The composite sheet provides a soft skin contact when the aforementioned inelastic fibrous layer is reduced in diameter and increased in apparent bulk due to elongation of constituting fibers as a result of plastic deformation. On the other hand, the increasing influence of the second factor lowers the percentage elastic extension of the composite sheet and thus narrows its possible range of elastic stretch and contraction, so that the composite sheet is made less elastically stretchable and contractible.